In the detection, diagnosis and treatment of diseases, it is highly important to simply and quickly detect the presence of certain ingredients contained in blood, lymph, urine and other body fluids while determining the amount thereof.
For example, quick and simple determination of the amount of glucose in a body fluid such as urine or blood is a prime desideratum to early detection, diagnosis and control of diabetes. Quick and simple determination of the amount of the protein in a body fluid, particularly urine, assumes an important role in the early detection, diagnosis and treatment of gastropathy. Accurate determination of the pH of a body fluid, particularly urine, can aid not only in detection of the presence of protein therein but also in confirmation of the possible bacteriuria which induces pyelitis, cystitis and like urosis.
As indicated above, it is of crucial importance to simply and quickly detect a variety of test-objective ingredients in a body fluid. For this purpose, a test device comprising a test reagent-impregnated filter paper affixed to a support has heretofore been used in most cases. Further, there have been attempts to develop test devices which can be obtained by a simplified process and is suitable for mass production. Such test devices have been produced by incorporating materials such as a polymeric binder and a water-absorptive carrier in a test reagent to prepare an ink composition suitable for printing or coating, applying the ink composition onto a support by printing (including coating), and drying the ink composition thus applied onto the support to form a test piece. The test reagent layer of the thus obtained test device for body fluids changes its tone depending upon the content of test-objective materials in a solution to be tested, and the content of the test-objective materials is detected by comparing a color formed by immersion in the solution to be tested with a tone table for criterion printed on a paper different from the test device.
On the other hand, when these test devices are immersed in a solution to be tested and thereafter the resulting color is compared with a separately provided tone table for criterion, the operations are cumbersome and the solution to be tested per se is colored. Accordingly, the change of the tone formed by the reaction of the test reagent with the test-purpose material in the solution to be tested is not accurately represented by the color of the test device; it is difficult to compare the color of the test device with the tone table for criterion; and an accurate test cannot be carried out in some cases. Thus, in order to solve such problems, a test device wherein a substrate of the test device is provided with a test reagent layer containing a test reagent, and a tone layer for criterion which is provided by printing a printing ink composition in the vicinity of said test reagent layer has been proposed.
As described above, when the test device comprising the test reagent layer and the tone layer for criterion both formed on the substrate is immersed in a solution to be tested, and the color of the test reagent layer is compared with the tone layer for criterion, it is possible to avoid a judgment error due to color formation of the solution to be tested or the like.
However, as described in the prior art, when the tone layer for criterion is printed on the substrate using conventional ink compositions, the following drawbacks occur. While uniform color formation occurs at the surface of the test reagent layer, the solution to be tested merely deposits on the printed surface of the tone layer in the form of droplets due to differences in surface tension between the printed surface of the tone layer and the surface of the test reagent layer as well as differences in physical shape or state of their surfaces. Accordingly, the tone of the tone layer becomes uneven and it is difficult to compare the color of the tone layer with the color of the test reagent layer.
Further, in the prior art test device for body fluids, a considerable difference exists between the water-absorption properties of the reagent layer and the tone layer, and therefore comparison of hues cannot be carried out under equivalent conditions. This results in reduced test precision.